The invention relates to a terminal-guidance or position-adjustment system for aircraft, particularly reconnaissance missiles equipped with computing facilities. In such a system a radio altimeter installed aboard the ircraft cooperates with a transponder installed on the ground at site A intended for the return of the aircraft or for its position adjustment. The radio altimeter is of the continuous-wave type in which the carrier is frequency-modulated in an essentially linear manner, and includes a transmitting aerial and a receiving aerial directed towards the ground. The transponder is of the pseudocontinuous-wave type and includes two-position switches for controlling radio-frequencies and receiving/transmitting aerial connections.
The invention is intended preferably for an aircraft possessing an inertial centre or any other system giving a similar accuracy and adequate computing facilities. A system of the above-identified type is known from French Patent Specification 2,435,866 (corresponding to U.S. Pat. No. 4,358,763).
Aerial-reconnaissance missiles are generally designed for departing from a base, covering a certain predetermined route, carrying out observations above certain zones, and returning to a base which may be the base from which they departed or another base corresponding to the end of the route. These various operations are performed automatically by means, on the one hand, of an inertial guidance device which enables the missile to "know" at every instant during flight its horizontal accelerations, speed and position and, on the other hand, of a radio altimeter indicating the height above the ground. The horizontal path and the height are programmed in advance and an on-board computer enables the intended position of the missile to be compared at any instant with the position indicated by the inertial guidance device and to make progressively the steering corrections necessary to keep the missile as close as possible to the preset intended path.
The path covered by the missile is on the order of several hundreds of kilometers and, although its inertial guidance device is very accurate, its position error at the arrival area is on the order of several hundreds of meters. However, it is desired to recover the missile or at the very least the information it has gathered in the course of its mission and this position inaccuracy may prove inconvenient both with regard to the difficulty of locating exactly what has to be recovered and what may be parachuted on the return of the device, and for the area to be set aside for this landing. Generally speaking, the aforementioned disadvantages are accepted and no terminal-guidance system is provided for the missile which remains independent from the start to the finish of its flight.